A video signal processor of a video tape recorder uses a noise canceler at a stage following a luminance/chrominance signal separator, for decreasing the level of the noise component included in, e.g., the luminance signal.
A noise canceler has a non-linear circuit for extracting a high-frequency component, which is assumed to be a noise component, from the luminance signal. A noise canceling component (processing signal) fetched by the non-linear circuit is input to a subtracter and is used to cancel the original noise component included in the luminance signal.
The characteristics of a non-linear circuit are important factors in accurately generating a noise canceling component. A non-linear circuit is constituted by a high-pass filter and a limiter. A noise canceling component is generated in the following manner. A high-frequency component included in a luminance signal is extracted by the high-pass filter, and a component of the extracted signal which is less than the limiter level is extracted by the limiter. The extracted signal is regarded as the noise canceling component.
An output gain of the overall non-linear circuit and the limiter level of the limiter cannot be independently adjusted. When the limiter level is adjusted, the output gain changes. As a result, the output gain of the noise canceling component depends on the amplification factor of the limiter.
When, e.g., an image quality controller is connected to the input of the noise canceler, the noise canceling operation by the noise canceler becomes incomplete.
An image controller extracts and amplifies a high-frequency component (including an edge emphasis component and a noise component) of a luminance signal, thereby correcting the edge of the image. In general, the level of an edge component is high and that of the noise component is low. When a noise canceler is connected to the output of the picture quality controller having these characteristics, the high-pass filter of the noise canceler extracts an amplified noise component and an edge emphasis component. In order to further extract the noise component from the noise component and the edge emphasis component (extracted signal) by the limiter, the limiter level must be increased. This is because the noise component is amplified by the picture quality controller. However, when the limiter level is increased, the edge emphasis component can be accidentally extracted.
As the result, the edge emphasis component emphasized by the picture quality controller is canceled by the subtracter.
In order to solve this problem, the limiter level might be lowered. When the limiter level is lowered, however, the output gain is decreased, as has been previously described. Then, the level of the noise canceling component in the subtracter becomes lower than that of the original noise component amplified by the picture quality controller, and noise cancellation becomes incomplete.
It is an object of the present invention to provide a video signal processor in which the output gain of a non-linear circuit and a limiter level can be independently adjusted, the characteristics and the gain of a processing signal component (e.g., a noise canceling component) fetched from the non-linear circuit can be arbitrarily adjusted, and accurate processing can be performed when a video signal is processed utilizing this processing signal component.